1. Field of the Invention
The present invention relates to a shift device adapted for a transmission in which pushing force applied to a sleeve can be amplified into larger pushing force acting on a synchronizer ring while gears of the transmission are shifted, thereby decreasing operating force necessary for a driver or an actuator.
2. Description of the Related Art
A shift device adapted for a transmission of this kind is disclosed in Japanese Unexamined Patent Application Publication No. 09-89002. In this shift devices, a plurality of lever members are provided between a hub and a synchronizer ring that is pressable to a fifth speed gear. When a transmission is shifted to a reverse position, operating force of a sleeve, which acts in a direction opposite to the fifth speed gear, is transmitted to the synchronizer ring due to reaction of the lever members so as to press the synchronizer ring to the fifth speed gear. This induces synchronization between the synchronizer ring and the fifth speed gear to decrease a rotation speed due to inertia of a clutch disc of an input shaft side, and then a reverse gear moving together with the sleeve is moved and engaged with reverse drive and driven gears without engagement noise.
In this reverse shift operation, the lever members are moved outwardly in a radial direction due to frictional torque generated by the synchronizer ring to block a movement of the sleeve until the synchronization of the fifth speed gear and the synchronizer ring ends.
After the synchronization ended, blocking force due to the frictional torque of the synchronizer ring vanishes. This enables the sleeve to move to the fifth speed gear to finish the shift operation to the reverse position, pressing and moving the lever members inwardly in the radial direction through slanting surfaces formed on inner splines of the sleeve.
In these shift operations, the lever members are pushed outwardly in the radial direction due to centrifugal force generated according to rotation thereof. This needs that the sleeve has to overcome the centrifugal force to press the lever members inwardly in order to further move after the synchronization ends. In a slow shift toward the fifth speed at high vehicle speed running, force to overcome the centrifugal force occasionally becomes larger than operating force necessary for the synchronization. Especially, in a case where a synchronizer device of the fifth speed is provided on an output shaft, operating force to overcome the centrifugal force becomes heavy as much as a driver feels uncomfortable because the synchronizer device rotates at higher speed than the device provided on an input shaft and the centrifugal force increases in proportion to square of rotational speed.
In order to improve the above-described drawback, the inventor suggested forming the inner splines of the sleeve to have smaller tilt angle so as to decrease force to overcome centrifugal force in Japanese Unexamined Patent Application Publication No. 2005-113975.
This suggestion, however, needs to overcome the centrifugal force acting on the lever members from the end of synchronization to the end of shift operation. Accordingly, a driver feels uncomfortable when he or she operates the shift device at high vehicle speed running.
It is, therefore, an object of the present invention to provide a shift device adapted for a transmission which overcomes the foregoing drawbacks and can remove the need for overcoming the centrifugal force acting on the lever members after the end of synchronization, thereby making a driver feel comfortable to operate the shift device at high vehicle speed running.